Manufacture of vulcanized rubber compounds



Patented Nov. 1, 1932 UNITED'ST-ATES PATENT OFFICE WILLIAM P. TER. HORST, OF NITRO, WEST VIRGINIA, ASSIGNOR TO THE RUBBER SERVICE LABORATORIES COMPANY, OF AKRON, OHIO, A. CORPORATION OF OHIO MANUFACTURE OF VULCANIZED RUBBER COMPOUNDS No Drawing. Original application filed January 20, 1927, Serial No. 182,416. Divided and this application filed October 27, 1927. Serial No. 229,271.

The present invention is directed to the manufacture of guanidine derivatives and more particularly to the use of such compounds as accelerators of the vulcanizatlon of rubber. The invention will be understood from the following description and examples wherein the invention is fully set forth and described.

Certain derivatives of guanidine have heretofore been employed as rubber vulcanization accelerators, particularly the mono, diand tri-phenyl and tolyl derivatives. Symmetrical tri-phenyl-guanidine was one of the first members of this series of compounds to be employed as an accelerator but its activity 1 is so much less than is that of the mono and (ii-substituted guanidines, that the compound has long ceased to be of any commercial importance to the rubber industry.

I have now discovered a new type of trisubstituted guanidines which comprise much more powerful vulcanization accelerators than are the tri-phenyl or tri-tolyl guanidines heretofore employed. The compounds I have manufactured and which I prefer to employ as accelerators, as shown by the examples' hereinafter set forth, comprise derivatives of tri-phenyl-guanidine, wherein the =N.G H group is replaced by various groups, of which one is the =N.NH.O H

' group, that is the characteristic grouping of phenyl-hydrazine. 1

A tri-substituted guanidine containing this grouping has been made by desulphurizing a thiourea, such as thiocarbanilide, by means of a suitable lead compound, such as litharge, white lead and the like in the presence of an amine containing the =N-NH' grouping, for example, phenyl-hydrazine. Preferably,

40 the reaction is carried out in thepresence of a small quantity of alcohol orrother suitable solvent. More specifically, approximately equi-molecular proportions, that is 228 parts of thiocarbanilide and 108 parts of phenyl l hydrazine, are placed in a suitable closed container, such as an autoclave, together with 250 parts of litharge and approximately 750 cu. cm. of 95% alcohol and the mass maintained at a temperature of approximately to C. for about twenty-four hours or, if desired, for a shorter time at a somewhat higher temperature, but the temperature employed is preferably below the boiling point of the solvent used.

When the reaction is completed, the mixture is withdrawn from the reaction vessel and is filtered while hot to remove the lead sludge from the solution. The residuum is washed with a small quantity of alcohol or with any other solvent corresponding to that employed in the reaction. The combined filtrate isthen run into approximately three times its volume of water slightly acidified preferably with hydrochloric acid. In case any thiocarbanilide remains unreacted, it is precipitated from the solution by this step. If any precipitate forms, it is removed by filtration. -Tl1e, filtrate is run into a cold solution of an alkali, such as caustic soda, whereby the guanidine product is precipitated. The product is then separated by filtration ofthe suspension and maythen' be washed or, if desired, may be further puri-, fled by solution in an acid, such as hydrochloric acid and then precipitated therefrom by means of caustic soda solution.

The product is separated from the suspension by filtration means and is then dried by any suitable process, such as in vacuo. Crystals of symmetrical di-phenyl-phenylimino-guanidine, having a light pink color, and possessing a melting point of from 128 to 130 C. are thereby produced.

Tri-substituted guanidines of a similar type have been obtained by employing other amines or amino derivatives in place of the phenyl-hydrazine mentioned in the example. Thus, one molecular proportion of thiocarbanilide has been heated under the condi' tions previously described with a desulphurizing agent, such as lead oxide in the pres-- ence of substantially one molecular proportion of ethylene-di-amine, C H (NH A suitable solvent such as alcohol, benzol and the like, is preferably employed. The resulting reaction product is then purified, preferably in the manner heretofore described.

Other similar products have been obtained by desulphurizing a di-substituted thiourea accelerator in the presence of such basic nitrogen-containing compounds as di-cyan-diamide, methyl amine, and the like. In a similar manner amines, such as ethylamine, butylamine, and other amines, preferably primary amines can be employed. Likewise, other thioureas than di-phenyl-thiourea mentioned in the examples, have been employed. Thus, the di-tolyl-thioureas, the di- Xylyl-thioureas and other di-substituted thioureas when treated in the manner as described, produced products included within my preferred class of tri-substituted guanidines.

The reaction products obtained by operating in the manner as set forth are seen to produce tri-substituted guanidines by the desulphurization of a di-substituted thiourea compound, and preferably such thiourea compounds as are themselves vulcanization accelerators, followed by the amidation of the desulphurized product by means of an ammonia derivative such as the amines and preferably a derivative of an amine containing the =NNH grouping. I have found that the most favorable results for the object desired are realized by amidating the desulphurized thiourea by employing for that purpose an amine possessing an electrolytic dissociation constant greater than 3.5X1O the dissociation constant of aniline at 18 by the hydrolytic method. In order that the tri-substituted gu'anidine obtained shall be efiective as a vulcanization accelerator, it is desirable that the compounds employed in the manufacture of the product, shall contain no groups of an acidic nature or other substituting groups that will materially decrease the basicity of the product.

Symmetrical di-phenyl-phenyl-imino-guanidine, that is, desulphurized diphenylnidine thiourea, amidated in the presence of phenyl-hydrazine has the following formula:

This and the other products hereinbefore mentioned as comprising my preferred class of vulcanization accelerators possesses the general formula N.R3R4

O=N.N.R1Rz

N.R5Ru

wherein R R and R represent hydrogen, an alkyl, or other group of non-acidic nature, and R R and R represent the same or different aryl groups, or substituted aryl groups. Thus, R R and R comprise such groups as the phenyl, tolyl, Xylyl, phenetidyl, anisidyl, di-menthyl-anilido, di-ethyl-anilido 011{ other substituted anilido groups, and the li e.

The tri-substituted guanidines of the type hereinbefore mentioned, that is, derivatives containing the wherein R represents preferably an hydrogen atom or alkyl group and R represents an aryl group, have been employed as accelerators of the rubber vulcanization process, as are shown by the following examples. Thus, a rubber compound, typical of a friction stock, was mixed in the well known manner and vulcanized. Similar rubber compounds were prepared by employing the wellknown (ii-substituted guanidines as accelerators and the physical characteristics of the vulcanized products were determined and prepared.

The mixes comprised the following ingredients in the proportions as indicated which represent parts by weight:

A B O Pale crepe rubber 100 100 100 Sulphur 3. 5 3. a 3. 5 Zinc oxide 5 5 5 Di-pheny1-guamd1ne 0.5 Di-o-tolyl-guaaidine 0. 5 Symmetrical di-pheuyl-phenyl-imiuo-guanidine 0.5

The physical characteristics of the vulcanized products are as follows:

Load neceslsary to t ffi f Tensile Elon- Time of cure Stock strength gation at break 30 minutes at a temper- A 119 ?75 986 2585 880 ature of 40 pounds of B 172 388 1550 3425 850 steam per sq. in. O 162 364 1405 3400 855 1 hour at a temperature A 208 450 1780 3175 810 of 40 pounds of steam B 269 713 3015 4005 770 per sq. in. O 252 600 2705 4175 795 A hard rubber was obtained by employing the following composition mixed in the ordinary manner:

20 parts of smoked sheet rubber, 20 parts of amber #2 rubber,

5 parts of lime,

15 parts of zinc oxide,

25 parts of sulphur,

10 parts of mineral rubber,

1 part of one of my new accelerators, such as symmetrical di-phenyl-phenyl-iminoguanidine.

81 parts of smoked sheet rubber,

20 parts of amber #2 rubber,

20.5 parts of zinc oxide,

19 parts of carbon black,

3.5- parts of mineral rubber,

1 part of a softener comprising a blended minoral and vegetable oil,

2 parts of sulphur, and

0.5 parts of one of my new type of accelerators, such as symmetrical .di-phenyl-phenylimino-guanidine. V

The rubber compound was vulcanized by heating in a press for approximately one hour at a temperature of 287" F., and upon testing was found to possess a modulus of elasticity at 500% elongation of 2805, a tensile strength at break of 37 85 pounds per square inch and an ultimate elongation of 620%.

Other compounds included in my new type of tri-substituted guanidines, have been employed as accelerators. Thus, a di-substituted thiourea accelerator, desulphurizedand amidated in the presence of ethylene-di-amine, of tetra-methyl-ammonium hydroxide, of pi peridine, and other basic organic compounds, possessing an electrolytic dissociation constant greater than 3.5 X 10 have all shown vulcanization accelerating properties when compounded in rubber mixes. These and other accelerators of this same type, can be employed in rubber compounds similar to those hereinbefore described or in other compounds as are apparent to those skilled in the art of rubber compounding.

The great superiority of my new class of tri-substituted guanidines, as compared with tri-phenyl guanidine as an accelerator is apparent from the following example, wherein the. ingredients employed represent parts by weight. 1 i V Smoked sheetrubber s 100 100 Zinc oxide 15 16 Sulphur 3 3 TIi-phenyi-gnanidine Symmetrical di plienyl-phenyl-iinino guanidine- 1 The above mixes werethen vulcanized and the cured product tested with the following results I r p ioaggnecesls ary to .7 i t i ii n ongw' Tensile Elon- Tune of cure T Stock I strength gatlon so imites at287 A a 147 402 669 s35 45 minutes at 287911;- '1 119 265' 705 1300 s40 The examples hereinbeforegiven are-to be understood as illustrative only and notat all limitative of the scope of my invention. Furthermore, my invention is not dependent upon the accuracy of any-theoriesorstatements advancedin explanation of the changes taking place in the ma nufacture or use of the preferred class of accelerators. The invention is limited solely by the following claims, appended .hereto'as' a part of this specification, wherein I intend to claim all novelty inherent in the invention as is permissible in View of the prior art. The dissociation constant hereinbefore mentioned is that obtained by the so-called hydrolytic method at 18 C.

The present application is a division of a copending application Serial No. 162,416, filed-January 20, 1927.

What I claim is:

1. The process of manufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator comprising a symmetrical di-aryl-aryl-imino-guanidine.

2. The process of manufacturing vulcanized hubber which comprises heating a mix ture of rubber and sulphur in the presence of an accelerator comprising symmetrical di-phenyl-phenyl-imino-guanidine.

3. The process of manufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the presence of an accelerator comprising the product obtained by desulphurizing di-phenyl-thiourea and amidating the desulphurized product in the presence of an aryl derivative of hydrazine.

4. The process of manufacturing vulcanized rubber which comprises heating a mixture of rubber and sulphur in the resence of an accelerator comprising a puri ed heat reaction roduct of di-phenyl-thiourea, phenyl-hy razine, a desulphurizing agent and a suitable solvent.

5. A vulcanized rubber product comprising the product resulting from heating rubber and sulphur in the presence of a tr'i-substituted-guanidine accelerator, said accelerator comprising a di-aryl-substituted thiourea vulcanization accelerator desi lphurized and amidated in the presence of an aryl derivative of hydrazine.

6. A vulcanized rubber product compris- 7 ing the product resulting from heating rubber and sulphur in the presence of a trisubstituted-guanidine accelerator, said accelerator comprising di-phenyl-thiourea desulphurized and amidated in the presence of phenyl-hydrazine.

7. A vulcanized rubber product comprising the product resulting from heating rubber andsulfur in the presence of a tri-substituted-guanidine accelerator, said accelerator' comprising a symmetrical di-aryl-arylimino guanidine.

:8, A vulcanized rubber product compris-' ing the product resulting from heating rubber and sulphur in the presence of a tri-substituted-guanidine accelerator, said accelerator comprising symmetrical di-phenyl phenyl-imino-guanidine.

In testimony whereof I hereunto afiix my signature.

WILLIAM P. TER HORST. 

